1. Field of the Invention
The present invention relates to a stable and flexible emulsion base for use in formulating cosmetic and dermatological compositions. More particularly, the present invention relates to stable and flexible emulsion bases with surfactant/emulsifier ratios that allow formulation of a broad range of cosmetic and dermatological compositions, specifically suncare compositions.
2. Description of the Related Art
Cosmetic and dermatological compositions, including suncare compositions, are commercially available in various forms, such as lotions, sprays, creams, gels, milks, and the like, and are well known in the art.
Formulators of such compositions generally start by combining various components together to develop, through trial and error, a composition that is stable and has the desired properties and form. These formulations typically involve a significant amount of time and expense with each attempt at a different combination of components and concentrations of those components.
Particularly, there are difficulty-formulating compositions that are stable and have properties desired for a specific type of composition. Compositions for different end uses require different basic properties, such as affinity of the composition for the skin and ability to be waterproof. The consumers of the compositions also demand certain properties, such as a luxurious, non-oily feeling on the skin. Consumers of suncare compositions, in particular, consider many factors when purchasing a suncare product, such as, the sun protection factor (SPF), how durable the product is after applying it over the skin, the shelf life of the product, and product form (i.e., lotions, gels, creams, and sprays). Another important and influential property of a suncare product considered by a consumer is how the product dispenses and how well the product spreads over the skin. Typically, consumers want a suncare product that does not drip and/or run from the dispenser orifice, from the hand during application, or once applied to the skin. Balancing these properties in a composition that is also stable over time can require a multitude of costly trials before a suitable final formulation is obtained.
This difficulty is evident in the formulation of suncare compositions, especially those having UV absorbing or blocking active agents. Many of the suncare active agents, such as avobenzone, are known to pose particular problems in formulating stable compositions that also have desirable aesthetic and skin feel properties. Furthermore, the addition of waterproofing agents to compositions is often highly desirable. This is the case with suncare products where the consumer expects UV protection to last for considerable time periods despite the typical use of suncare products in outdoor activities that involve either water or perspiration. However, the addition of waterproofing agents is also known to produce difficulties in formulating stable compositions.
Attempts have been made to provide base formulations to which active agents, typical excipients, and emollients can be easily added to form cosmetic and dermatological compositions with decreased formulation and production expense. However, designing a base formulation that is stable, while providing the flexibility to adjust the base formulation and/or produce final compositions that have properties over wide ranges, is very difficult. A particular difficulty arises in balancing the types and concentrations of emulsifiers and surfactants in the base formulation needed to provide the desired properties in an oil-in-water (O/W) emulsion. Stability of such O/W emulsions can typically be enhanced by increasing the viscosity, which can be achieved by the addition of hydrophilic compounds such as certain emulsifiers and gums. However, finding the proper balance between greater stability and compositions that have unworkable thicknesses has heretofore not been satisfactorily achieved. A base formulation that also allows for ease and flexibility in the addition of waterproofing agents engenders further difficulty in design.